Expandable intervertebral implant

ABSTRACT

An expandable intervertebral implant is provided for insertion into an intervertebral space defined by adjacent vertebrae. The expandable intervertebral implant includes a pair of outer sleeve portions and an inner core disposed between the outer sleeve portions. Movement of the inner core relative to the outer sleeve portions causes the outers sleeve portions to deflect away from each other, thereby engaging the expandable intervertebral implant with the vertebrae and adjusting the height of the intervertebral space.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. patent application Ser. No. 15/235,160 filed Aug. 12, 2016, which is a continuation application of U.S. patent application Ser. No. 14/565,611 filed Dec. 10, 2014, which is a continuation application of U.S. patent application Ser. No. 12/936,466 filed Oct. 5, 2010 now issued as U.S. Pat. No. 8,936,641, which is a National Stage of International Application Serial No. PCT/US2009/039501, filed Apr. 3, 2009, which claims the benefit of U.S. Provisional Application Ser. No. 61/042,724, filed on Apr. 5, 2008, the disclosure of each of which is hereby incorporated by reference as if set forth in its entirety herein.

FIELD OF THE INVENTION

This disclosure relates generally to intervertebral implants, and in particular relates to an intervertebral implant that can expand to create a desired spacing and/or angular orientation of adjacent vertebrae.

BACKGROUND OF THE INVENTION

Degenerative disc disease or degeneration of a vertebral body often results in a loss of disc height, which in turn can cause facet and nerve impingement, among other things. One standard of care is to replace the damaged intervertebral disc with an intervertebral implant or a damaged portion or an entire vertebral body with an intervertebral implant.

Thus, an intervertebral implant may be inserted into the intervertebral disc space of two adjacent vertebral bodies or into the space created by removal of portions of, or the entire, vertebral body after removal of damaged portions of the spine. Preferably, the intervertebral implant restores the spine, as much as possible, to a natural state. That is, the implant preferably restores the original height of the intervertebral disc and thus the original distance between the two adjacent vertebral bodies or vertebral bodies in various levels of the spine. These implants are sized and shaped to fill at least the physiological height between the vertebral bodies and are inserted through a relatively narrow and small incision with nerves and vascular structure proximate sides of the incision. Accordingly, it is advantageous to develop an implant that may be inserted in a reduced size or configuration and expanded when positioned between the vertebrae to minimize the required incision and limit the potential for the implant to contact the neural and vascular structure during implantation.

It is desirable to construct an intervertebral implant that restores the spine to its natural state, is relatively compact during insertion and may be expanded when positioned between adjacent vertebrae. It is also desirable to construct an expandable intervertebral implant that may be inserted and expanded utilizing the same instrument.

BRIEF SUMMARY OF THE INVENTION

The following Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description of Illustrative Embodiments. This Summary is not intended to identify key features or essential features of the invention, nor is it intended to be used to limit the scope of the invention. Reference is made to the claims for that purpose.

Certain embodiments are directed to an expandable intervertebral implant for insertion into an intervertebral disc space and expandable from an initial position to an expanded position. The expandable intervertebral implant includes a linkage that includes a plurality of links connected in a longitudinal direction. Each link includes an outer sleeve having a first outer sleeve portion and a second outer sleeve portion that is movable with respect to the first outer sleeve portion. The second outer sleeve portion defines a first engagement surface that is sloped with respect to the longitudinal direction. Each link further includes an inner core disposed between the first and second outer sleeve portions. The inner core defines a second engagement surface that is sloped with respect to the longitudinal direction, wherein the second engagement surface abuts the first engagement surface. Relative movement between the inner core and the second outer sleeve portion along the longitudinal direction causes the first engagement surface to ride along the second engagement surface, thereby causing the second outer sleeve portion to deflect away from the first outer sleeve portion in a direction substantially perpendicular to the longitudinal direction.

Additional features and advantages will be made apparent from the following detailed description of illustrative embodiments with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following detailed description, is better understood when read in conjunction with the appended drawings. There is shown in the drawings example embodiments, in which like reference numerals correspond to like reference numerals throughout. The expandable intervertebral implant and related methods are not limited to the specific embodiments and methods disclosed, and reference is made to the claims for that purpose.

FIG. 1A is a perspective view of an expandable intervertebral implant constructed in accordance with one embodiment installed in an intervertebral space;

FIG. 1B is a perspective view similar to FIG. 1A, but with the intervertebral implant installed in the intervertebral space in accordance with an alternative embodiment

FIG. 2A is a sectional side elevation view of the expandable intervertebral implant illustrated in FIG. 1 constructed as a linkage that includes a plurality of expandable intervertebral links in accordance with one embodiment, wherein the implant is in a first contracted position;

FIG. 2B is an enlarged portion of the expandable intervertebral implant illustrated in FIG. 2A;

FIG. 3A is a side elevation view of an expandable intervertebral link of the intervertebral implant illustrated in FIG. 2A;

FIG. 3B is a side elevation view of the expandable intervertebral link similar to FIG. 3A, but constructed in accordance with an alternative embodiment;

FIG. 3C is a side elevation view of the expandable intervertebral link similar to FIG. 3A, but constructed in accordance with another alternative embodiment;

FIG. 4A is a sectional end elevation view of the expandable intervertebral link illustrated in FIG. 3A;

FIG. 4B is a sectional end elevation view of an expandable intervertebral link similar to that illustrated in FIG. 4A, but constructed in accordance with an alternative embodiment;

FIG. 5 is a sectional side elevation view of the expandable intervertebral link illustrated in FIG. 2A;

FIG. 6 is a sectional side elevation view of the expandable intervertebral implant illustrated in FIG. 5A, connected to an insertion device.

FIG. 7 is a sectional side elevation view of the expandable intervertebral implant illustrated in FIG. 6, but illustrated in a second vertically expanded position;

FIG. 8A is a top plan view of the expandable intervertebral implant illustrated in FIG. 7, including a retainer that secures various components of the expandable intervertebral implant;

FIG. 8B is a sectional end view of the expandable intervertebral implant as illustrated in FIG. 8A;

FIG. 8C is an enlarged view of a portion of the expandable intervertebral implant illustrated in FIG. 8B;

FIG. 9A is a sectional end view of the expandable intervertebral implant similar to FIG. 8B, but showing a retainer constructed in accordance with an alternative embodiment;

FIG. 9B is a side elevation view of the expandable intervertebral implant illustrated in FIG. 9A;

FIG. 10 is a sectional side elevation view of an expandable intervertebral implant similar to FIG. 6, but configured to provide a lordotic outer profile when expanded, in accordance with an alternative embodiment;

FIG. 11 is a sectional side elevation view of the expandable intervertebral implant illustrated in FIG. 10, but showing the implant in a vertically expanded position;

FIG. 12A is a top plan view of the expandable intervertebral implant illustrated in FIG. 10;

FIG. 12B is an enlarged side elevation view of a portion of the expandable intervertebral implant illustrated in FIG. 12A;

FIG. 13 is a side elevation view of an expandable intervertebral implant including a second retainer constructed in accordance with an alternative embodiment;

FIG. 14 is a sectional side elevation view of an expandable intervertebral implant similar to FIG. 10, but configured to define a lordotic outer profile when expanded, in accordance with an alternative embodiment;

FIG. 15A is a top sectional view of an expandable intervertebral implant similar to that illustrated in FIG. 6, but further configured for lateral expansion in accordance with an alternative embodiment, wherein the expandable intervertebral implant is shown in a laterally contracted position;

FIG. 15B is a sectional end view of the expandable intervertebral implant illustrated in FIG. 15A including a retainer constructed in accordance with one embodiment;

FIG. 15C is a sectional end view of the expandable intervertebral implant similar to FIG. 15B, but showing the expandable intervertebral implant in a vertically and laterally expanded position;

FIG. 15D is a sectional end view of the expandable intervertebral implant similar to FIG. 15C, but including a retainer constructed in accordance with an alternative embodiment;

FIG. 16A is a side elevation view of an expandable intervertebral implant coupled to a biasing member of an insertion device in accordance with one embodiment;

FIG. 16B is a side elevation view of the expandable intervertebral implant illustrated in FIG. 16A, but with the biasing member coupled to additional components of the insertion device, wherein the insertion device is illustrated in a disengaged position;

FIG. 16C is a side elevation view of the expandable intervertebral implant as illustrated in FIG. 16B, but showing the insertion device in an engaged position;

FIG. 17A is a side elevation view of the expandable intervertebral implant as illustrated in FIG. 16C, but showing the insertion device including a central sleeve having a coupling member that locks the insertion device in the engaged configuration;

FIG. 17B is a side elevation view of the central sleeve illustrated in FIG. 17A;

FIG. 17C is a top plan view of the central sleeve illustrated in FIG. 17B;

FIG. 18A is a top plan view of an expandable intervertebral implant coupled to an angulated insertion device constructed in accordance with an alternative embodiment;

FIG. 18B is a top plan view of the expandable intervertebral implant coupled to the angulated insertion device illustrated in FIG. 18A, showing the insertion device in an angulated position;

FIG. 19A is a sectional side elevation view of an expandable intervertebral implant shown in an expanded position; and

FIG. 19B is a sectional side elevation view of the expandable intervertebral implant illustrated in FIG. 19A, but showing projecting portions removed after the implant has achieved the final expanded position.

DETAILED DESCRIPTION OF THE INVENTION

Certain terminology is used in the following description for convenience only and is not limiting. The words “right”, “left”, “lower” and “upper” designate directions in the drawings to which reference is made. The words “inwardly” or “distally” and “outwardly” or “proximally” refer to directions toward and away from, respectively, the geometric center of the expandable implant, instruments and related parts thereof. The words, “anterior”, “posterior”, “superior,” “inferior” and related words and/or phrases designate preferred positions and orientations in the human body to which reference is made and are not meant to be limiting. The terminology includes the above-listed words, derivatives thereof and words of similar import.

Referring to FIG. 1A, an expandable intervertebral implant 20 is shown installed into an intervertebral disc space 22 defined by a pair of adjacent, or neighboring, upper and lower vertebrae 24. The expandable intervertebral implant 20 can be configured to fuse with the vertebrae 24. The vertebrae 24 can be lumbar vertebrae that define an anterior side AS, an opposing posterior side PS. The vertebrae 24 further define opposing lateral sides LS that are disposed on opposing sides of a central medial axis M-M that extends along a mediolateral direction. The vertebrae 24 are illustrated as being spaced along a caudocranial axis C-C. The expandable intervertebral implant 20 extends generally along a longitudinal direction L, a lateral direction A, and a transverse direction T.

Various structure is therefore described as extending horizontally along a longitudinal direction “L” and lateral direction “A”, and vertically along a transverse direction “T”. The housing is elongate in the longitudinal direction L. Unless otherwise specified herein, the terms “lateral,” “longitudinal,” and “transverse” are used to describe the orthogonal directional components of various components. The directional terms “inboard” and “inner,” “outboard” and “outer,” and derivatives thereof are used herein with respect to a given apparatus to refer to directions along the directional component toward and away from the geometric center of the apparatus.

It should be appreciated that while the longitudinal and lateral directions are illustrated as extending along a horizontal plane, and that the transverse direction is illustrated as extending along a vertical plane, the planes that encompass the various directions may differ during use. Accordingly, the directional terms “vertical” and “horizontal” are used to describe the expandable intervertebral implant 20 and its components as illustrated merely for the purposes of clarity and illustration.

In the illustrated embodiment, the longitudinal direction L extends in an anteroposterior direction, the lateral direction A extends in the mediolateral direction, and the transverse direction T extends in the caudocranial direction. It should be appreciated, however, that the directions defined by the expandable intervertebral implant 20 could alternatively be oriented at any desirable angle between 0° and 180° with respect to the various directions defined by the vertebrae 24. For instance, the longitudinal and lateral directions of the implant could be oriented at any desirable angle between 0° and 180° with respect to the mediolateral and anteroposterior directions. As will become appreciated from the description below, the expandable intervertebral implant 20 can be inserted into the disc space 22 in an anterior direction, a posterior direction, or any alternative direction between 0° and 180° with respect to the anterior and posterior sides.

For instance, FIG. 1B illustrates the expandable intervertebral implant 20 installed into the intervertebral space 22 in an orientation that is 180° rotated with respect to the orientation illustrated in FIG. 1A. In this regard, it should be appreciated that the implant 20 can be inserted into the intervertebral space 22 from the anterior or posterior direction, or a direction that is angularly offset from the anterior or posterior direction. When inserting the implant 20 into the intervertebral space 22, for instance from the posterior, posterior anatomical elements can be removed, such as ligaments, a part or all of the lamina, the posterior arch, and some or all of the facet joints that are aligned with the vertebral space that receives the implant. While one implant 20 is illustrated as being inserted into the intervertebral space 22 in FIG. 1A, and a pair of implants 20 as being inserted into the intervertebral space 22 in FIG. 1B, any desired number of implants 20 can be inserted into a given intervertebral space as desired, such as between one and four implants. It should further be appreciated that one or more implants 20 can be installed into the intervertebral space 22 when performing a corpectomy or hemicorpectomy.

Referring now to FIGS. 2A, 3A, and 4A, the expandable intervertebral implant 20 can be provided as a longitudinally elongate linkage 26 that includes one or more links 28. The implant 20 can be made from any suitable biocompatible radiolucent or metallic material, such as titanium. The links 28 of the linkage 26 can be substantially similarly or identically constructed unless otherwise indicated. Each link includes an outer sleeve 30 formed from a pair of vertically opposing upper and lower outer sleeve portions 30A and 30B. The outer sleeve portions 30A and 30B each define a laterally elongate cross-beam 31 connected to a pair of outer legs 33 that each project transversely inward from the opposing outer lateral ends of the cross beams 31. Thus, the upper sleeve portion 30A includes legs 33 that project down from the laterally outer ends of the corresponding cross-beam 31, and the lower sleeve portion 30B includes legs 33 that project up from the laterally outer ends of the corresponding cross-beam 31. When the link 28 is in a first or initial contracted position, the inner transverse ends of the laterally aligned legs 33 can abut each other as illustrated so as to minimize the height of the implant 20 prior to installation into the intervertebral space 22, or they can alternatively be spaced apart.

The cross-beams 31 can each define respective vertebral engagement surfaces 32, such that the vertebral engagement surface of the upper sleeve portion 30A is an upwardly-facing surface, and the vertebral engagement surface of the lower sleeve portion 30B is a downwardly-facing surface. Each vertebral engagement surface 32 is configured to abut the corresponding upper and lower adjacent vertebrae 24.

Each outer sleeve portion 30A and 30B can include a plurality of teeth 34 projecting transversely out from the respective vertebral engagement surfaces 32. The teeth 34 can be laterally elongate, and can be arranged as a plurality of longitudinally spaced rows 36 as illustrated. The teeth 34 can have a substantially constant height across the plurality of rows 36, thereby defining a substantially linear toothed profile as illustrated in FIG. 3A. Alternatively, the teeth 34 can define a nonlinear profile across the rows. For instance, as illustrated in FIG. 3B, the rows of teeth of one or more links 28 can define a bowed profile, or a convexity, whereby the teeth 34 of the longitudinally middle rows have a height greater than the teeth of the longitudinally outer rows. The profile can be symmetrical or asymmetrical about a lateral axis passing through the longitudinal midpoint of the link 28.

Alternatively or additionally, referring to FIG. 4A, one or more of the rows 36 of teeth 34, up to all of the rows of teeth, can be bowed along the lateral direction, such that the laterally middle portions of the teeth 34 have a height that is greater than the laterally outer portions of the teeth. The profile can be symmetrical or asymmetrical about a longitudinal axis passing through the lateral midpoint of the link 28. Thus, the teeth 34 can define a profile that is convex, or bowed, along more than one direction. While the teeth 34 are shown as being laterally elongate, it should be appreciated that the teeth 34 can alternatively be discontinuous in a lateral direction across the vertebral engagement surfaces 32 in a lateral direction. For instance, referring to FIG. 4B, a second plurality of teeth 34 can project out from the vertebral engagement surfaces 32 along the lateral direction. Thus each row 36 may include one or more teeth 34 so as to form an array of laterally spaced and longitudinally spaced teeth 34 along the vertebral engagement surfaces 32. The teeth 34 can be in substantial vertical alignment along a lateral axis, or can be bowed as shown in FIG. 4B to define a convex profile along the lateral direction such that laterally central teeth 34 have a height greater than that of the laterally outer teeth of a given row 36. Alternatively or additionally, the teeth 34 can be bowed as shown in FIG. 3B to define a convex profile along the longitudinal direction.

The teeth 34 can assist in roughening the vertebral surface to assist in fusing the expandable intervertebral implant to the adjacent vertebrae, can provide a surface that grips against the vertebrae, and can also define an increased surface area that fuses with the adjacent vertebrae with respect to a flat vertebral engagement surface. Alternatively, one or both of the opposing vertebral engagement surfaces 32 can be substantially smooth, or non-toothed, along both the lateral and longitudinal directions, as illustrated in FIG. 3C. The smooth surface can extend substantially along a longitudinal-lateral plane, or can be bowed in either or both of the lateral and longitudinal directions.

With continuing reference to FIG. 2A, the linkage 26 can include one or more links 28, such as a plurality of adjoined links 28 as illustrated. Each link 28 can include a lateral cross beam 31 and a pair of opposing transverse legs 33 in the manner described above. Each link 28 can define a generally rectangular or square with straight or curved corners, edges, and surfaces, or any suitable alternative geometric shape. The linkage 26 defines a longitudinal front end 27 and an opposing longitudinal rear end 29. The rear end 29 of the linkage 26 can be geometrically configured for insertion into the intervertebral disc space 22. For instance, the cross beams of the link 28 disposed at the rear end 29 of the linkage can be curved transversely inward along a direction from front end 27 toward the rear end 29, thereby providing a guide surface when inserting the implant 20 into the intervertebral disc space 22.

Adjacent links 28 can be integrally connected or can alternatively be discreetly fastened to each other at a coupling location using any suitable mechanical or adhesive coupling member. For instance, a coupling member 35 can project longitudinally out from each leg 33 of adjacent links 28 toward the adjacent link 28, such that a coupling member 35 of the upper sleeve portion 30A of one link 28 is attached to a corresponding coupling member 35 of the upper sleeve portion 30A of an adjacent link 28. Likewise, a coupling member 35 of the lower sleeve portion 30B of one link 28 is attached to a corresponding coupling member 35 of the lower sleeve portion 30B of an adjacent link 28. The coupling members 35 can be flexible or rigid, and can be integrally formed with, or discreetly connected to, the corresponding legs 33. The linkage 26 can include any number of links 28 as desired, such that the upper sleeve portions 30A of each link 28 are connected, and the lower sleeve portions 30B of each link 28 are connected.

Referring now to FIGS. 2A and 5, the cross beam 31 of each outer sleeve portion 30A and 30B defines an outer vertebral engagement surface 32 as described above, and further defines an opposing transverse inner engagement surface 40 that extends laterally between the opposing transverse legs 33. The inner engagement surface 40 is sloped vertically so as to define an angle θ with respect to a longitudinal axis L-L that can be between 0° and 90°, for instance between about 10° and about 50°, such that the engagement surface 40 of each outer sleeve portion slopes transversely in along a longitudinal direction from the rear end 29 toward the front end 27 of the linkage 26. Thus, the inner engagement surface 40 of the upper sleeve portion 30A slopes vertically down along a longitudinal direction from the rear end 29 toward the front end 27, and the inner engagement surface 40 of the lower sleeve portion 30B slopes vertically up along a longitudinal direction from the rear end 29 toward the front end 27.

The engagement surfaces 40 of the upper sleeve portions 30A can define an angle greater θ or less than that of the engagement surfaces 40 of the lower sleeve portions 30B, thereby causing the upper sleeve portion 30A to expand at a higher or lower expansion rate, respectively, relative to the lower sleeve portion 30B. In this regard, it should be appreciated that the angle θ0 of one of the inner engagement surfaces 40 relative to the longitudinal axis L-L could be zero, while the angle θ of the other engagement surface 40 relative to the longitudinal axis L-L is non-zero, thereby causing only the outer sleeve portion of the other engagement surface to expand during operation.

The inner engagement surfaces 40 of each link 28 can be aligned with, and extend parallel to, the engagement surfaces 40 of the other links 28 of the linkage 26. Thus, the outer sleeve 30 of each link 28 can extend transversely a distance at its front end greater than at its rear end. Each link 28 can further include an engagement member as one or more projections or that extends transversely in from the engagement surfaces 40. The projections can be in the form of ridges, teeth, or like structure that is configured to mate with a complementary structure to fixes the implant in an expanded position. In the illustrated embodiment, the projections are shown as reverse angled teeth 44 that project transversely in from the engagement surface 40. Thus, for the purposes of description, the engagement member, or one or more projections, is referred to herein as teeth.

The teeth 44 project down from the engagement surface 40 of the upper sleeve portion 30A, and teeth project up from the engagement surface 40 of the lower sleeve portion 30B. The teeth 44 can define a root end 45 that is substantially in-line with the corresponding engagement surfaces 40, and triangular tips 46 that are transversely offset from the engagement surface. Adjacent tips 46 can be spaced apart any desired distance, such as between about 0.5 mm and about 5 mm. The teeth 44 of each link 28 can be substantially identically sized and shaped, such that a line connecting the tips 46 of adjacent teeth 40 extends parallel to the engagement surface 40. The outer sleeve portions 30A and 30B further define pockets 43 disposed between and defined by adjacent teeth 44. The pockets 43 thus have a size and shape substantially identical to the adjacent teeth 44 that define the pockets 43.

Each link 28 defines an internal void 38 that extends transversely between opposing cross beams 31 and laterally between opposing legs 33 of each outer sleeve portion 30A and 30B. The linkage 26 includes an inner core 50 that is disposed within the internal void 38 of each link 28, and is retained by the outer sleeve portions 30A and 30B. The inner core 50 can abut the transverse inner surfaces 40 of the cross beams 31 such that, during operation, longitudinal movement of the inner core 50 relative to the outer sleeve 30 causes the outer sleeve 30 to expand in a first direction, such as the vertical direction (see FIG. 7) and alternatively or additionally a second direction perpendicular to the transverse or vertical direction, such as the horizontal direction (see FIGS. 15A-C).

In the embodiment illustrated in FIGS. 2A-2B, the inner core 50 includes a core body 52 that defines opposing lateral surfaces that can face or abut the legs 33 of the outer sleeve, and opposing transverse outer, or upper and lower, engagement surfaces 54. The portion of the inner core 50 disposed within one of the links 28 can be integrally connected or alternatively fastened to the portions of the inner core 50 that are disposed in the other links 28 of the linkage 26 using any suitable mechanical or adhesive fastening member.

When the inner core 50 is installed in the internal void 38 of the outer sleeve 30, the engagement surfaces 54 can mate with, or abut, the corresponding sloped engagement surfaces 40 of the outer sleeve portions 30A and 30B. The engagement surfaces 54 are thus transversely sloped with respect to the longitudinal axis L-L, and thus extend parallel to the corresponding engagement surfaces 40. The inner core 50 can further include an engagement member as one or more projections that extend transversely out from the engagement surfaces 54. The projections can be in the form of ridges, teeth, or like structure that is configured to mate with a complementary structure to fix the implant in an expanded position. In the illustrated embodiment, the projections are shown as reverse angled teeth 56 that project transversely out from the engagement surfaces 54. Thus, for the purposes of description, the engagement member, or one or more projections, is referred to herein as teeth 56.

The teeth 56 can be sized and shaped substantially identical with respect to teeth 44, so as to mate with teeth 44. The teeth 56 define a root end that is substantially in-line with the corresponding engagement surfaces 54, and triangular tips 60 that are transversely offset from the engagement surface. The teeth 56 are identically sized and shaped, such that a line connecting the tips 60 of adjacent teeth 56 extends parallel to the engagement surface 54. Thus, the teeth of the inner core 50 become transversely inwardly disposed along a direction from the rear of the link 28 toward the front of the link 28. The inner core body 52 further defines pockets 57 disposed between and defined by adjacent teeth 56. The pockets 57 thus have a size and shape substantially identical to the adjacent teeth 56 that define the pockets 57.

With continuing reference to FIG. 2B, the teeth 44 are sized and shaped to interlock with mating teeth 56, and reside in the pockets 57 defined between adjacent teeth 56. Likewise, the teeth 56 are sized and shaped to interlock with mating teeth 44, and reside in the pockets 43 defined between adjacent teeth 44. The teeth 44 and 56 can define a sawtooth shape that is undercut such that the tips 46 and 60 of interlocking teeth 44 and 56 overlap each other a distance D, which can be greater than 0 mm and less than or equal to 2 mm. Accordingly, a transverse compressive force applied to the link 28 causes the teeth 44 and 56 to cam along each other to an interlocked position, such that interference between the tip ends 46 and 60 resists vertical separation of the outer sleeve 30 from the inner core 50 during insertion of the implant 20 into the intervertebral space. Moreover, as the implant 20 is inserted into the disc space 22, the bodily tissue will apply a forward longitudinal force against the outer sleeve 30, thereby biasing the teeth 44 and 56 into their interlocked position, whereby motion of the core 50 relative to the outer sleeve 30 is permitted in the longitudinally forward direction, but prevented in a longitudinally rearward direction.

The opposing tips 46 and 60 of interlocking teeth 44 and 56 can be spaced a transverse distance so as to define a height H that can be within a range between 0 mm and about 3 mm. The teeth 44 and 56 can further define an angle θ2 between about 10° and about 50° with respect to the longitudinal axis L-L.

Referring now to FIG. 6, the linkage 26 can be coupled to an insertion tool 70, which includes a biasing member 64, an inner holding sleeve 72, and an outer holding sleeve 74. The biasing member 64 is operable to move the inner core member 50 longitudinally forward relative to the outer sleeve 30. In the illustrated embodiment, the inner core body 52 defines an internal longitudinally elongate bore 62 that is sized and shaped to receive the biasing member 64, which can be provided as a longitudinally extending rod or wire 66 connected to a transverse stopper 68 at one longitudinal end of the wire 66. The wire 64 can be made from vitalium, titanium, or the like. The stopper 68 is sized and shaped to abut the rear surface of the inner core 50, but not the outer sleeve, of the rearmost link 28, and the wire 66 can extend through the bore 62 of all inner core bodies 52 along the linkage 26, and project forward from the front end 27 of the linkage. The wire 66 can be held in place inside the bore 62 by an interference fit or any suitable fixation mechanism.

The inner annular holding sleeve 72 surrounds the wire 66 at a location forward from the front end 27 of the linkage 26, and can guide the wire 66 during operation. The wire 66 can be pulled in a longitudinal forward direction relative to the inner holding sleeve 72 such that the inner holding sleeve 72 abuts the front end of the core body 52 of the front-most link. The engagement of the inner holding sleeve 72 and the core body 52 allows a user to maintain control of the position of the implant 20 during insertion into the intervertebral space 22 as tension is applied to the wire 66.

The outer annular holding sleeve 74 is configured to abut the front end of the forwardmost outer sleeve 30 at a location that is out of transverse alignment with the core body 52. The outer holding sleeve 74 provides reciprocal biasing member that is operable to provide a biasing force that is equal and opposite to the force applied from the biasing member 64 to the core 50. In this regard, the outer holding sleeve 74 can be referred to as a brace member.

Accordingly, as a first force F₁ is applied to the wire 66 along a longitudinally forward direction, the stopper 68 applies a corresponding longitudinally forward biasing force to the rear link 28. The outer holding sleeve 74 applies a force F₂ into the outer linkage sleeve 30 that is equal and opposite with respect to the force F₁. The force F₁ applied to the wire 62 thus causes the inner core 50 to translate longitudinally forward with respect to the outer sleeve 30.

Referring also to FIG. 7, as the inner core 50 translates forward with respect to the outer sleeve 30, the engagement surfaces 40 ride along the complementary engagement surfaces 54, thereby causing the outer sleeve portions 30A and 30B to deflect vertically away from each other. As the outer sleeve portions 30A and 30B deflect away from each other, the intervertebral implant 20 expands in the transverse, or vertical, direction. The slope of the upper and lower mating engagement surfaces 40 and 54 determines the rate at which the upper and lower sleeves 30A and 30B expand, respectively.

As the inner core 50 moves in the forward direction with respect to the outer sleeve 30, the tips 46 and 60 of the engagement members, or teeth 44 and 56, cam over each other, thus causing the height of the implant 20 to increase in increments substantially equal to the height H of the teeth 44 and 56. Once a desired height is achieved and the biasing force is removed from the wire 62, the engaging teeth 44 and 56 can allow slight relative motion of the outer linkage sleeve 30 relative to the inner core 50 in the longitudinally forward direction, which can cause the outer teeth 34 of the sleeve to scuff the inner surfaces of the adjacent vertebrae 24, thereby facilitating fusion of the sleeve portions 30A and 30B to the vertebrae 24.

Once the teeth 44 and 56 become interlocked, relative motion between the inner core 50 and the outer sleeve 30 is prevented in the absence of the application of another biasing force to the cable 66. It should thus be appreciated that the linear forward motion of the inner core 50 relative to the outer sleeve 30 causes the intervertebral implant 20, or outer sleeve portions 30A and 30B, to expand from an initial, or relaxed position having a first height, to a second or an expanded position having a second height that is greater than the first height. The teeth 44 and 56 provide engagement members that prevent the outer sleeve portions 30A and 30B from contracting toward each other once the intervertebral implant 20, sleeve outer portions 30A and 30B, have reached the desired expanded position. It should be appreciated that while the engagement surfaces 40 and 54 of each link 28 each include a plurality of corresponding teeth, each engagement surfaces 40 and 54 could alternatively comprise one or more teeth.

During operation, the implant 20 is inserted into the intervertebral space 22 in the initial position, and subsequently expanded to a second expanded position so as to abut and position the adjacent vertebrae 24 to a desired vertical position that causes the intervertebral space to achieve a desired height. The intervertebral implant 20 can thus be referred to as an intervertebral spacer that causes the intervertebral space 22 between adjacent vertebrae to increase to a desired caudocranial height. An autograft or bone substitute can be placed around the implant 20 in the intervertebral space 22 if desired.

It should be appreciated that, as shown in FIG. 6, the core body 52 of the rear link 28 can be sized having a longitudinal length that is substantially longer than that of the corresponding outer sleeve 30. As a result, the core 50 can project rearward with respect to the sleeve 30 of the rearmost link 28 by an offset distance “O” when the implant 20 is in the initial or relaxed position. The offset distance O can be preselected based, for instance, on the slope of the engagement surfaces 44 and 54 and the desired expansion of the outer sleeve 30, such that once the implant 20 has reached the desired final height, the rear surface of the core 50 can be substantially flush with the rear surface of the outer sleeve 30 the rear link 28, as shown in FIG. 7.

Moreover, FIG. 6 shows the front end of the core body 52 of the front linkage 28 as being substantially flush with the front end of the outer sleeve 30 of the front linkage 28 when the implant 20 is in the initial position. Accordingly, as shown in FIG. 7, when the implant is in the expanded position, the front end of the core body 52 of the front linkage 28 extends forward from the front end of the outer sleeve 30 of the front linkage 28. It should be appreciated, however, that the front end of the core body 52 of the front linkage 28 could alternatively be recessed with respect to the front end of the outer sleeve 30 of the front linkage 28 a distance equal to the offset distance O when the implant 20 is in the initial position. Accordingly, when the implant 20 is in the expanded position, the front end of the core body 52 of the front linkage 28 could be substantially flush with the front end of the outer sleeve 30 of the front linkage 28.

Referring now to FIGS. 8A-C, the expandable intervertebral implant 20 can include a retainer member in the form of one or more, such as a plurality of, bands 84 that are configured to apply a compressive retention force against the links 28 that can assist in maintaining the structural integrity of the implant 20 as the implant 20 is inserted into the intervertebral space 22 and expanded to the vertically expanded position. In particular, the linkage 26 can include laterally opposing transverse slots 82 that extend vertically through the coupling members 35. The coupling members 35 can include a lateral portion that extends in a laterally extending groove 86 disposed between adjacent links 28.

A metallic or elasticized band 84 can be inserted through the laterally opposing slots 82 and sit in the grooves 86 such that the band 84 surrounds the legs 33 of the outer sleeve portions 30A and 30B. The band 84 can include terminal ends 85A and 85B that form an interlocking tongue-and-groove. Thus, the terminal ends 85A and 85B can be clipped together, and the terminal ends can be placed inside one of the slots 82 so as to reduce the possibility that the band 84 would be inadvertently separated. The bands 84 can apply a compressive force that biases the outer sleeve portions 30A and 30B against each other and against the inner core 50, thereby assisting in the retention of the teeth 44 and 56 in their interlocked configuration. The bands 84 can be radiolucent so as to provide an indication of the position and angular orientation of the implant 20 during the implantation procedure.

Referring now to FIG. 9A-B, the expandable intervertebral implant 20 can include a retainer member constructed in accordance with an alternative embodiment. In particular, the legs 33 do not define a transverse slot extending vertically therethrough. Instead, an elasticized band 88 can be stretched over one or more of the links 82 and inserted into the groove 86. The elasticity of the band 88 can apply a compressive force that biases the outer sleeve portions 30A and 30B against each other and against the inner core 50, thereby assisting in the retention of the teeth 44 and 56 in their interlocked configuration. The plurality of bands 88 can be radiolucent so as to provide an indication of the position and angular orientation of the implant 20 during the implantation procedure.

Referring now to FIG. 10, the expandable intervertebral implant can be constructed such that the vertebral engagement surfaces 32 define a lordotic profile when the implant 20 is in the expanded position. In accordance with the illustrated embodiment, the slope S of the engagement surfaces 40 and 54 relative to the longitudinal axis L-L of each link 28 vary from link to link. Thus, the opposing engagement surfaces 40 and 54 of one link are angled, or not parallel, with respect to the corresponding opposing engagement surfaces 40 and 54 of an adjacent link. For instance, the slope of each interfacing engagement surfaces 40 and 50 of each link 28 relative to the longitudinal axis L-L has a magnitude that decreases along a direction from the rear link 28 toward the front link 28. Thus, the magnitude of the slope of the complementary engagement surfaces 40 and 54 of a given link 28 is greater than that of forwardly disposed links 28, and less than that of rearwardly disposed links 28.

Accordingly, as the implant 20 expands, the outer sleeve portions 30A and 30B of each link 28 will become vertically displaced at different rates. In the illustrated embodiment, the rate of outer sleeve vertical displacement will decrease in a direction from the rear link 28 toward the front link 28. It should, of course, be appreciated that the slope of the engagement surfaces 40 and 50 of each link could alternatively decrease in a direction from the front link 28 toward the rear link 28 such that the rate of vertical displacement would decrease in a direction from the front link 28 toward the rear link 28. Alternatively still, the middle links 28 can expand at a rate that is greater than or less than the forward and rearward spaced links 28.

In the embodiment illustrated in FIG. 10, the vertebral engagement surfaces 32 of the opposing outer sleeve portions 30A and 30B can be substantially flat in the longitudinal direction. The slope of opposing vertebral engagement surfaces 32 of each link 28 can vary from link to link. Thus, the vertebral engagement surfaces 32 of one link are angled, or not parallel, with respect to the engagement surfaces 32 of an adjacent link. It can also be said that the engagement surfaces 32 of each link 28 are sloped at an angle with respect to the longitudinal direction that is different than the angle at which the engagement surfaces 32 of the other links are sloped relative to the longitudinal direction.

The opposing engagement surfaces 32 of the outer sleeve portions 30A and 30B of a given link 28 can be equal and opposite relative to the longitudinal axis L-L. As illustrated, the vertebral engagement surfaces 32 of the links 28 each define a slope having a magnitude with respect to the longitudinal axis L-L that decrease from link to link as the slope of the corresponding engagement surfaces 40 and 50 increase when the implant 20 is in the initial position. Thus, in the illustrated embodiment, the slope of each of the vertebral engagement surfaces 32 of the links 28 has a magnitude that decrease in direction from the front end 27 of the linkage 26 toward the rear end 29 of the linkage. The magnitude of the slope of the opposing vertebral engagement surface 32 of a given link 28 is greater than that of rearwardly disposed links 28, and less than that of forwardly disposed links. Alternatively, the slope of the opposing vertebral engagement surfaces 32 of each link 28 could be substantially identical from link to link.

Referring now to FIG. 11, when the inner core 50 is moved longitudinally forward relative to the outer sleeve 30 to move the implant from the initial position to the expanded position in the manner described above, the links 28 expand at different rates. In particular, a given link 28 expands at a faster rate than forwardly disposed links, and at a rate slower than rearwardly disposed links. As a result, when the intervertebral implant 20 is in the expanded position illustrated in FIG. 11, the opposing outer sleeve portions 30A and 30B of each link 28 have expanded a distance that is greater than those of forwardly disposed links, and less than those of rearwardly disposed links. Thus, the implant 20 defines vertebral engagement surfaces 32 that are sloped transversely outward with respect to the longitudinal axis L-L in a direction from the front end 27 toward the rear end 29. Moreover, the vertebral engagement surfaces 32 of each outer sleeve portion 30A and 30B are in line with the vertebral engagement surfaces 32 of the other links 28 of the linkage 26, thereby creating reliable engagement surfaces with the vertebrae 24.

Referring to FIGS. 12A-B, it should be appreciated that the links 28 can be coupled so as to permit relative vertical motion between adjacent links. Accordingly, the adjacent links 28 can be coupled by a joint, such as a tongue-and-groove joint 90. The joint 90 includes a pair of first laterally opposing engagement members 92 attached to one of the adjacent links 28. The engagement members 92 extend vertically, and each includes a beveled surface 94 that slopes laterally inward along a direction longitudinally away from the link 28. The other of the adjacent links 28 includes a second laterally elongate engagement member 96 that extends laterally between the opposing engagement members 92. The engagement member extends vertically, and includes laterally opposing beveled surfaces 98 that slopes laterally outward along a direction longitudinally away from the link 28. The beveled surfaces 94 and 98 engage each other to interlock the adjacent links with respect to longitudinal separation, while allowing for relative vertical motion along the beveled surfaces 94 and 98, and thus relative vertical motion between the adjacent links 28. A retainer member, such as band 88, can further be inserted into one or more of the grooves 86 that separate the adjacent links 28 so as to further maintain the structural integrity of the linkage 26 during use in the manner described above.

Alternatively or additionally, the expandable intervertebral implant 20 can include an auxiliary retainer such as a flexible band 100 as illustrated in FIG. 13. The band 100 defines a body 101 that extends generally in the longitudinal direction, and defines a pair of opposing terminal ends 102 that each define connection locations that can be connected to an outer sleeve portion 30A or 30B of a different one of the plurality of links 28. The terminal ends 102 can define a hinged connection with respect to the outer sleeve portion, or can define a fixed connection such that the flexibility of the band 100 allows the terminal ends 102 and other connection locations to rotate relative to the body 101. The bands 100 can be fastened to the outer sleeve portions 30A and 30B using any suitable mechanical fastener.

In the illustrated embodiment, the terminal ends 102 of one band 100 are connected to the laterally outer surfaces of the upper sleeve portions 30A of the longitudinally outermost links 28. The terminal ends 102 of another band 100 are connected to the laterally outer surfaces of the lower sleeve portions 30B of the longitudinally outermost links 28. A pair of substantially identical bands can be connected to the opposing outer lateral surfaces of the upper and lower sleeve portions 30A and 30B. Thus, the bands 100 provide a longitudinal compressive force to all links 28 disposed between the terminal band ends 102. Alternatively, the bands 100 can be connected to one or more, up to all, links 28 that are disposed between the terminal ends 102 of the bands 100.

It should be appreciated that FIGS. 10-13 illustrate the intervertebral implant 20 configured to produce a lordotic profile in accordance with one embodiment, and that alternative embodiments can be provided to create a lordotic profile. For instance, referring to FIG. 13, the vertebral engagement surfaces 32 of each outer sleeve portions 30A and 30B are aligned with the vertebral engagement surfaces 32 of the corresponding outer sleeve portions 30A and 30B of the adjacent links. Thus, the vertebral engagement surfaces 32 of each outer sleeve portion 30A are aligned and parallel to each other, and the vertebral engagement surfaces 32 of each outer sleeve portion 30 b are aligned and parallel to each other. Moreover, the engagement surfaces 32 of each outer sleeve portion 30A and 30B can be sloped with respect to the longitudinal axis L-L. In the illustrated embodiment, the engagement surfaces 32 define a slope S₁ that is angled transversely out from the longitudinal axis L-L in a direction from the front end 27 of the linkage 26 toward the rear end of the linkage. It should be appreciated, however, that the engagement surfaces 32 could alternatively slope transversely in from the longitudinal axis L-L in a direction from the front end 27 of the linkage 26 toward the rear end of the linkage.

Furthermore, the engagement surfaces 40 and 50 of each outer sleeve portion 30A are aligned with and extend parallel to the engagement surfaces 40 and 50 of the outer sleeve portions 30A of the other links 28. Likewise, the engagement surfaces 40 and 50 of each outer sleeve portion 30B are aligned with and extend parallel to the engagement surfaces 40 and 50 of the outer sleeve portions 30B of the other links 28. Accordingly, as the implant is expanded to the expanded position illustrated in FIG. 13, each link 28 is displaced transversely outward at the same displacement rate of the other links, and the vertebral engaging surfaces 32 maintain the lordotic profile described above.

Thus, the expandable intervertebral implant 20 is configured to expand along the transverse direction and can be further configured such that the vertebral engaging surfaces 32 can define a lordotic profile when engaged with the vertebrae. Alternatively or additionally, the intervertebral implant 20 can be configured such that the vertebral engaging surfaces 32 of the links 28 combine to define a nonlinear shape, such as a curved convex shape having outer longitudinal ends that are disposed transversely inward with respect to a longitudinal middle portion.

Referring to FIG. 15A, the opposing axially inner surfaces of the legs 33 of each outer sleeve portion 30A and 30B can define laterally opposing, and vertically extending, engagement surfaces 110 that can be longitudinally elongate, and sloped laterally with respect to the longitudinal axis L-L at any desired angle as described above with respect to the transverse angle formed between inner engagement surface 40 and the longitudinal axis. Accordingly, that the engagement surface 110 of each sleeve portion slopes laterally out from the longitudinal axis along a direction from the front end 27 toward the rear end 29 of the linkage 26. In this regard, it should be appreciated that the laterally sloped engagement surface 110 can be constructed as described above with respect to the transversely sloped engagement surface 40. However, the cross beam 31 of each outer annular sleeve is discontinuous along the lateral direction, such that each leg of the outer sleeve portions 30A and 30B is free to move relative to the other leg of the same outer sleeve portion in the lateral direction. Each leg of a given outer sleeve portion is free to move in the transverse direction with respect to the legs of the opposing outer sleeve portion in the manner described above.

The engagement surfaces 110 of the upper sleeve portions 30A can define an angle greater or less than that of the other, and can further define an angle greater or less than that of the engagement surfaces 110 of the lower sleeve portions 30B, thereby causing one lateral side of the outer sleeve 30 to expand laterally at a higher or lower expansion rate, respectively, relative to the other lateral side of the outer sleeve 30. In this regard, it should be appreciated that the angle of one or both of the of the inner engagement surfaces 110 relative to the longitudinal axis L-L could be zero, while the angle of the other engagement surface 110 relative to the longitudinal axis L-L is non-zero, thereby causing only one lateral side of the outer sleeve to expand laterally during operation.

The engagement surfaces 110 of each link 28 can be aligned with, and extend parallel to, the engagement surfaces 110 of the other links 28 of the linkage 26. Thus, the outer sleeve 30 of each link 28 can extend laterally at its front end a greater amount than at its rear end. Each link 28 can further include an engagement member in the form of reverse angled teeth 114 that project laterally inward from the engagement surface 110. The lateral teeth 114 can be constructed in the manner described above with reference to the transverse teeth 44.

The inner core body 52 defines laterally outer engagement surfaces 124 that are configured to engage the engagement surfaces 110 of the upper and lower sleeves 30A and 30B. The inner core body 52 can extend vertically a sufficient distance such that each engagement surface 124 can engage with the pair of complementary engagement surfaces 110 on each lateral side of the sleeve 30. The engagement surfaces 124 can be laterally sloped with respect to the longitudinal axis L-L, and can thus extend parallel to the corresponding engagement surfaces 110. The lateral engagement surfaces 124 can be constructed as described above with respect to the transverse engagement surfaces 54. The inner core 50 can further include an engagement member in the form of reverse angled teeth 126 that project laterally out from the engagement surfaces 124. The teeth 126 can be sized and shaped substantially identical with respect to teeth 114, so as to mate with teeth 114. The teeth 126 can be constructed in the manner described above with respect to teeth 56.

As illustrated in FIG. 15B, the outer sleeve portions 30A and 30B can be retained by a retainer such as a plurality of bands 84 in the manner described above. Slots 82 can extend vertically through both pairs of opposing laterally outer legs 33, and the band 84 can be inserted into the slots 82 and placed in the groove 86 in the manner described above to apply compressive retention forces onto the linkage, thereby assisting in securing the structural integrity of the expandable intervertebral implant 20. Alternatively, as illustrated in FIG. 15D, the retainer may be provided as an elasticized band 88 that is placed in the groove 86 in the manner described above to apply laterally and transverse compressive securing forces.

Referring now to FIGS. 15A and 15C, as the inner core 50 moves in the forward direction with respect to the outer sleeve 30, the engagement surfaces 40 ride along the complementary engagement surfaces 54, and the teeth 44 and 56 cam over each other, thereby causing the outer sleeve portions 30A and 30B to incrementally deflect vertically away from each other in the manner described above. Furthermore, the engagement surfaces 110 ride along the complementary engagement surfaces 124, and the teeth 114 and 126 cam over each other, thereby causing the laterally outer portions of the outer sleeve 30 to incrementally deflect laterally away from each other from a first laterally contracted position to a second laterally expanded position. It should be appreciated that the engagement surfaces 110 and 124 can have a slope that is greater than or less than the slope of engagement surfaces 40 and 54, such that the implant 20 can expand vertically at a greater rate or a lesser rate than the implant 20 expands laterally.

It should be appreciated that a kit can be provided that includes all or a portion of the expandable intervertebral implant 20 constructed in accordance with any of the embodiments described herein. For example, the kit can include one or more of the components of the expandable intervertebral implant, such as the upper and lower outer sleeve portions 30A and 30B, the inner core 50, bands 84 and 88, and a plurality of links 28. The one or more components included in various kits can have one or more varying characteristic such as size and/or shape. For instance, a first kit can be provided having one or more components, for instance outer sleeve portions 30A and 30B, the inner core 50, bands 84 and 88, and a plurality of links 28, that have a different size or shape to accommodate different expansion rates, different longitudinal and/or lateral lengths, and different directions of expansion, for instance transverse expansion alone or coupled with lateral expansion. Some components in a given kit may permit the implant 20 to produce a lordotic profile in the manner described above, while other components in the kit may permit the implant to produce a horizontal upper and lower vertebrae-engaging surface. The kit can further include components of the insertion tool 70 as will now be described.

In particular, referring now to FIGS. 16A-C, the insertion tool 70 can be configured to engage the intervertebral implant 20 such that the implant 20 may be inserted into the intervertebral space 22 and subsequently expanded in the manner described above. Once the intervertebral implant is disposed in the intervertebral space, the insertion tool can include biasing members that apply a biasing force to the implant, thereby causing the implant to expand in any manner as described above. Once the implant 20 has reached the desired expansion position, the insertion tool 70 may be disengaged from the implant 20.

The insertion tool 70 can include the inner annular holding sleeve 72, the biasing member 64 that extends inside the inner annular holding sleeve 72, and the outer annular holding sleeve 74 that receives the inner annular holding sleeve 72. Once the holding member 70 is moved to position such that the inner annular holding sleeve 72 abuts the inner core 50 and the outer annular holding sleeve 74 abuts the outer sleeve 30, a force F1 can be applied to the wire 66 that causes the implant to expand in the manner described above.

Referring to FIGS. 17A-C, the inner annular holding sleeve 72 can include a longitudinally elongate body 151 having a threaded engagement surface 152 at a distal end that is configured to be threadedly received in the outer annular holding sleeve 74. The inner annular holding sleeve 72 can include a proximal end having a forked abutment member 154. The forked abutment member 154 can include a pair of spaced prongs 156 that are configured to abut the inner core 50 in the manner described above. The wire 62 can thus extend through the inner core 50 of each link 28, between the prongs 156 and through the inner annular holding sleeve 72. The free end of the wire that extends through the inner annular holding sleeve can be coupled to any suitable tensioning device configured to apply a biasing force sufficient to cause the intervertebral implant 20 to expand.

Referring now to FIGS. 18A-B, the insertion tool 70 can further include an angulated member 158 that is connected between the forward end 127 of the linkage 26, and the proximal ends of the inner and outer holding sleeves 72 and 74. The angulated member 158 can include a rectangular block 159, a cylindrical body 160 rigidly attached to the block 159, and a bore 162 extending through the body 160 sized to receive the wire 66. The wire 66 can thus extend through the linkage 56, the cylindrical body 160, and the inner sleeve 72. The outer sleeve 73 can define a bore 164 extending longitudinally therethrough, and a directional rod 166 extending through the bore 164. The directional rod 166 defines a proximal end that is pivotally coupled to the block 159 at a connection location 158 that is laterally offset with respect to the lateral center of the cylindrical body 160.

During operation, the rectangular block 159 abuts the inner core 50, and the directional rod 166 can be moved longitudinally forward and rearward, thereby causing the cylindrical body 160 to rotate relative to the proximal ends of the inner and outer sleeves 72 and 74. As the cylindrical body 160 rotates, the rectangular block 159 causes the intervertebral implant to change its angular orientation in the horizontal plane defined by the lateral and longitudinal directions. As illustrated, movement of the rod 166 in a forward direction causes the intervertebral implant 20 to pivot in a clockwise direction, while movement of the rod 166 in a rearward direction causes the implant to pivot in a counterclockwise direction. It should be appreciated, of course, that the rod 166 could alternatively be connected to the rectangular block 159 at a location that causes the intervertebral implant 20 to pivot in the clockwise direction when the rod is moved rearward, and counterclockwise when the rod is moved forward.

During operation, the longitudinal position of the rod 166 can be determined prior to inserting the intervertebral implant 20 into the disc space 22 so as to define an angular orientation of the implant 20 relative to the inner and outer sleeves 72 and 74. The angular orientation of the implant 20 allows the implant to be inserted into the body cavity along an anteroposterior directional approach or a posterior-anterior directional approach, while at the same time orienting the implant such that the longitudinal axis L defines a desired angle with respect to the anterior and posterior directions when the implant is inserted into the disc space 22. Once the intervertebral implant 20 has been inserted into the disc space 22, the wire 66 can be moved longitudinally forward to cause the implant 20 to expand in the transverse direction T alone, or in the transverse direction T and simultaneously the lateral direction A. Moreover, as the implant 20 expands in either the transverse direction T alone or in the transverse direction T simultaneously with the lateral direction A, the opposing transverse vertebral-engaging surfaces 32 can remain flat and parallel with each other, or can define an angular orientation configured to restore lordosis to the vertebrae 24 in the manner described above.

Finally, referring to FIGS. 19A and 19B, once the implant 20 has been positioned in the intervertebral space 22 and expanded to the desired expanded position, the outer sleeve 72 can be removed out of engagement with the intervertebral implant, and the remaining portions of the tool 70 can be removed by cutting the portion of the intervertebral body 50 that protrudes from the front end 127 of the linkage 26 along a cut line 168 along the lateral-transverse plane LT. The cut can be made in from opposing directions, for instance using reciprocal blades at opposing locations, such that the blades can cut through the inner core body 52 and the wire 66 and cause the body 50 to crimp around the wire 66. Alternatively, the inner core body 52 can be cut in any desired manner, and a separate crimping tool can be used to crimp the body 50 around the wire 66 after the body 50 and wire 66 have been cut, thereby securing the wire and preventing the wire 66 from being inadvertently removed after the surgical procedure has been completed.

The embodiments described in connection with the illustrated embodiments have been presented by way of illustration, and the present invention is therefore not intended to be limited to the disclosed embodiments. Furthermore, the structure and features of each the embodiments described above can be applied to the other embodiments described herein. Accordingly, those skilled in the art will realize that the invention is intended to encompass all modifications and alternative arrangements included within the spirit and scope of the invention, as set forth by the appended claims. 

What is claimed:
 1. An expandable intervertebral implant insertable into an intervertebral disc space and expandable from an initial position to an expanded position, the expandable intervertebral implant comprising: a first outer portion defining a first bone contacting surface, the first outer portion elongate along a central axis, the first outer portion including a plurality of first outer links and a first flexible coupling connected between first and second ones of the first outer links that are adjacent to each other, such that the first one of the first outer links is movable with respect to the second one of the first outer links; a second outer portion defining a second bone contacting surface, the second outer portion elongate along the central axis including a plurality of second outer links and a second flexible coupling connected between first and second ones of the second outer links that are adjacent to each other, such that the first one of the second outer links is movable with respect to the second one of the second outer links, wherein the first and second outer portions combine to define a footprint of the implant with respect to a direction perpendicular to the central axis that has a first size when the implant is in the initial position; and a movable member configured to be positioned between the first and second outer portions, such that translation of the movable member along the central axis in a single direction relative to both 1) the first and second ones of the first outer links, and 2) the first and second ones of the second outer links causes the footprint to increase along the direction when the implant is in the expanded position.
 2. The expandable intervertebral implant as recited in claim 1, wherein the first and second outer portions are spaced from each other along a transverse direction, and the direction perpendicular to the central axis is defined by the transverse direction.
 3. The expandable intervertebral implant as recited in claim 2, wherein the first and second outer portions move away from each other along the transverse direction so as to increase the footprint.
 4. The expandable intervertebral implant as recited in claim 1, wherein the movable member comprises an inner core that has a height greater than a height of a gap between the first and second outer portions when respective sides of the upper and lower members abut each other.
 5. The expandable intervertebral implant as recited in claim 4, wherein the inner core comprises opposed ramped surfaces that bear against the first and second outer portions so as to increase a height of the implant.
 6. The expandable intervertebral implant as recited in claim 4, wherein the inner core comprises projections that interlock with respective pockets of the first and second outer portions.
 7. The expandable intervertebral implant as recited in claim 1, wherein the first and second outer portions are spaced from each other along a transverse direction, and the direction perpendicular to the central axis is also perpendicular to the transverse direction.
 8. The expandable intervertebral implant as recited in claim 7, wherein the first and second outer portions move away from each other along the direction perpendicular to the central axis.
 9. The expandable intervertebral implant as recited in claim 7, wherein the movable member comprises a stopper at one end, and a rod that extends out the other end, such that pulling on the rod causes the stopper to apply a biasing force to the first and second outer portions that increases the footprint.
 10. An expandable intervertebral implant insertable into an intervertebral disc space and movable from an initial position to an expanded position, the expandable intervertebral implant comprising: a first outer portion defining a first bone contacting surface, the first outer portion including a plurality of first outer links and a first flexible coupling connected between first and second ones of the first outer links that are adjacent to each other, such that the first one of the first outer links is movable with respect to the second one of the first outer links, and; a second outer portion defining a second bone contacting surface, the second outer portion elongate along the central axis including a plurality of second outer links and a second flexible coupling connected between first and second ones of the second outer links that are adjacent to each other, such that the first one of the second outer links is movable with respect to the second one of the second outer links, wherein the first and second bone contacting surfaces are opposite each other along a transverse direction; and an inner core configured to be positioned between the first and second outer portions, such that translation of the inner core between the first and second outer portions causes the links of the first and second outer portions to move away from each other along the transverse direction, thereby moving the implant from the initial position to the expanded position, wherein the inner core comprises projections that are received in respective recesses of the first and second outer portions as the inner core translates between the first and second outer portions to expand the implant from the initial position to the expanded position.
 11. The expandable intervertebral implant as recited in claim 10, wherein the inner core comprises ramped surfaces that bear against the first and second outer portions, respectively, so as to expand the implant from the initial position to the expanded position.
 12. The expandable intervertebral implant as recited in claim 10, wherein the inner core comprises projections that interlock with respective pockets of the first and second outer portions.
 13. An expandable intervertebral implant that is insertable into an intervertebral disc space and expandable from an initial position to an expanded position, the expandable intervertebral implant comprising: a first outer portion defining opposed ends spaced from each other along a longitudinal direction, the first outer portion further defining a first bone contacting surface, wherein the first outer portion defines a first pair of sloped engagement surfaces that are spaced from each other along the longitudinal direction; a second outer portion defining opposed ends spaced from each other along the longitudinal direction, the second outer portion further defining a second bone contacting surface spaced from the first bone contacting surface along a transverse direction that is substantially perpendicular to the longitudinal direction, wherein the second outer portion further defines first and second sloped engagement surfaces that are spaced from each other along the longitudinal direction, and the second bone contacting surface defines an orientation relative to the first bone contacting surface; and an inner core disposed between the first and second outer portions, the inner core defining a third pair of sloped engagement surfaces that face the first outer portion and are spaced from each other and aligned with each other along the longitudinal direction, and a fourth pair of sloped engagement surfaces that face the second outer portion and are spaced from each other and aligned with each other along the longitudinal direction, wherein (i) movement of the inner core relative to the first and second outer portions causes a) each of the third pair of sloped engagement surfaces to ride along each of the first pair of sloped engagement surfaces, respectively, and b) each of the fourth pair of sloped engagement surfaces to ride along each of the second pair of sloped engagement surfaces, respectively, thereby causing the first and second outer portions to deflect away from each other along the transverse direction from the initial position to the expanded position, (ii) the relative orientation of the second bone contacting surface with respect to the first bone contacting surface remains constant before, during, and after deflection of the first and second outer portions away from each other along the transverse direction, (iii) the implant defines a height from the first bone contacting surface to the second bone contacting surface along the transverse direction, and the expandable intervertebral implant is designed such that when the expandable intervertebral implant is in the initial position, the height is a minimum height such that the implant is unable to achieve a height less than the minimum height via movement of the inner core relative to each of the first and second outer portions along the longitudinal direction, and (iv) when the expandable intervertebral implant is in the expanded position, the first and second outer portions are prevented from moving toward each other in a direction from the expanded position to the initial position while (a) the third pair of sloped engagement surfaces is in abutment with the first pair of sloped engagement surfaces, respectively, and (b) the fourth pair of sloped engagement surfaces is in abutment with the second pair of sloped engagement surfaces, respectively.
 14. The expandable intervertebral implant as recited in claim 13, wherein the movement of the inner core relative to the first and second outer portions is in a single direction. 